Why would you offer them bespoke, relevant images for half the price of generic stock?
I don't see them a bespoke - it doesn't appear that he was commissioned. It appears that he has taken them, they have been seen, he has been asked if they can be used. The going rate for "generic stock" is what the market will pay. That is dictated by manly by the agencies who sell them. The photographer will see less than half of the sale.
If the photographer doesn't know how much to charge, he could open an account with Alamy / Corbis etc, tell the buyer to go through the buying process of selecting the picture's use, paying Alamy £100, and then only seeing £45 of the sale.
I see that, advising the bloke to use the market sellers as a guide for the value of a picture, as good advice. By giving his customer the option of cutting out an unnecessary middle man, (in those circumstances) and giving his customer the best value, the photographer creates exactly the same income from the pictures.
How is that devaluing stock photography?
What are the other options? "The Race Team" turns out to be Yamaha Inc, the picture is featured on their home page in every territory worldwide for the next 3 years, and the poor bloke gets screwed over by forum advice of "just charge him a tenner, that's what I got last time....etc..etc..etc.." type of replies.
I stand by my post - find out the value of the image by using industry standards. What he does with it from there is up to him.